A French magazine's decision to publish cartoons depicting a naked Prophet Mohammad triggered a new wave of fears at embassies in Europe, even as anger at the west continued to sweep through the Muslim world.

France announced Wednesday it will close 20 embassies in Arab and Muslim nations after the weekly Charlie Hebdo published the controversial cartoons. The images threaten to further inflame Muslim protesters and terror groups, who have demonstrated against the U.S. at embassies around the world since an anti-Islam film went viral last week.

The French Foreign Ministry issued a travel warning Wednesday urging French citizens in the Muslim world to exercise "the greatest vigilance," avoiding public gatherings and "sensitive buildings" such as those representing the West or religious sites. At the same time, the country -- which has western Europe's largest Muslim population -- plunged into new debate over the limits to free speech in a modern democracy.

France's prime minister said freedom of expression is guaranteed, but cautioned that it "should be exercised with responsibility and respect."

Foreign Minister Laurent Fabius warned that Charlie Hebdo could be throwing "oil on the fire," but said it's up to courts to decide whether the magazine went too far.

The cartoons could extend a wave of violence linked to a trailer for an amateurish film called the "Innocence of Muslims," which portrays the prophet as a fraud, a womanizer and a child molester, has killed at least 30 people in seven countries.

The U.S. Ambassador to Libya, Christopher Stevens, and three other Americans, were also killed in a strike on the U.S. Consulate in Benghazi -- though it remains unclear whether the violence was a coordinated attack by terrorists.

On Wednesday, several hundred lawyers protesting the movie forced their way into an area in Pakistan's capital that houses the U.S. Embassy and other foreign missions. The United States temporarily closed its consulate in an Indonesian city because of similar demonstrations, and hundreds protested the film in Sri Lanka's capital and burned effigies of President Obama.

The magazine's crude cartoons played off the film and ridiculed the violent reaction to it. Riot police took up positions outside the offices of the magazine, which was firebombed last year after it released an edition that mocked radical Islam.

Charlie Hebdo's chief editor, who goes by the name of Charb and has been under police protection for a year, defended the cartoons.

"Muhammad isn't sacred to me," he said in an interview at the weekly's offices, on the northeast edge of Paris amid a cluster of housing projects. "I don't blame Muslims for not laughing at our drawings. I live under French law; I don't live under Quranic law."

Government authorities and Muslim leaders urged calm.

"This is a disgraceful and hateful, useless and stupid provocation," Dalil Boubakeur, rector of the Grand Paris Mosque, told The Associated Press. "We are not Pavlov's animals to react at each insult."

A small-circulation weekly, Charlie Hebdo often draws attention for ridiculing sensitivity around the Prophet Muhammad, and an investigation into the firebombing of its offices last year is still open. The magazine posted a statement online saying its website had been hacked.

Abdallah Zekri, president of the Paris-based Anti-Islamophobia Observatory, said his group is considering filing a lawsuit against the magazine.

"People want to create trouble in France," he said. "Charlie Hebdo wants to make money on the backs of Muslims."

Meanwhile, seven Egyptian Coptic Christians living abroad, including Nakoula Bassely Nakoula, who made the "Innocence of Muslims" film, and Florida Pastor Terry Jones, will be tried, presumably in absentia, by a criminal court for insulting Islam over the trailer, Egypt's public prosecutor said Tuesday.

The prosecutor said that convictions could be punishable by the death penalty, and called for the eight individuals to handed over to Egypt.

Fox News' Leland Vittert and the Associated Press contributed to this report.